1. Field of the Invention
The present invention relates to granules based on pyrogenically produced aluminium oxide, to the process for the production thereof, and to the use thereof.
2. Description of the Background
It is known to produce pyrogenic aluminium oxide by means of elevated temperature or flame hydrolysis from AlCl3 (Ullmanns Enzyklopxc3xa4die der technischen Chemie, 4th edition, volume 21, page 464 (1982)).
Pyrogenic aluminium oxides are distinguished by extreme fineness, correspondingly elevated specific surface area (BET), very high purity, spherical particle shape and the absence of pores. Due to these properties, there is increasing interest in pyrogenically produced aluminium oxides as supports for catalysts (D. Koth et al, Chem. Ing. Techn. 52, 628 (1980)). For this application, the pyrogenically produced aluminium oxide is mechanically formed, for example by means of tabletting machines.
The object accordingly arose of providing sprayed granules of pyrogenically produced aluminium oxide which may be used for a variety of purposes, such as, for example, catalyst supports.
It is another object of the invention to provide methods of making and using such granules, as well as to provide compositions containing the same.
The objects of the present invention, and others, may be accomplished with granules comprising, i.e., based on, pyrogenically produced aluminium oxide having the following physicochemical characteristics:
The objects of the invention may also be accomplished with granules comprising pyrogenicaly produced aluminium oxide having the following physicochemical characteristics:
The objects of the invention may also be accomplished with a process for the production of the granules described above, comprising dispersing pyrogenically produced aluminium oxide is dispersed in water and then spray drying.
The objects of the invention may also be accomplished with a composition selected from the group consisting of a catalyst support, glass, ceramic, abrasive agent, polishing agent, cosmetic, toner powder, paint and lacquer, which comprises the granules described above, and with methods of making the composition.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the detailed description below.
As described above, the average grain diameter of the inventive granules may be 5.0 to 150 xcexcm and the tamped density may be 300 to 1200 g/l. In a preferred embodiment of the invention, the granules may exhibit an average grain diameter of 5.0 to 45 xcexcm and a tamped density of 300 to 550 g/l. These ranges for the average grain diameter include all specific values and subranges therebetween, such as 10, 15, 20, 25, 50, 75, 100 and 125 xcexcm. These ranges for the tamped density include all specific values and subranges therebetween, such as 350, 400, 500, 600, 700, 800, 900, 1000 and 1100 g/l.
The granules according to the invention may be produced by dispersing pyrogenically produced aluminium oxide in water, spray drying it and optionally heat treating the granules obtained at a temperature of 150 to 1100xc2x0 C. for a period of 1 to 8 hours. This temperature range includes all specific values and subranges therebetween, such as 200, 250, 300, 400, 500, 600, 700, 800, 900, and 1000xc2x0 C. This range for the time period includes all specific values and subranges therebetween, such as 2, 3, 4, 5, 6, and 7 hours.
The educt used may comprise an aluminium oxide as described in Ullmanns Enzyklopxc3xa4die der technischen Chemie, 4th edition, volume 21, page 464(1982), incorporated herein by reference. Another educt which may be used is a pyrogenically produced aluminium oxide with an elevated surface area, which exhibits a BET specific surface area of greater than 115 m2/g, and the Sears value is greater than 8 ml/2 g.
Measured on a sample weight of 16 g, the dibutyl phthalate absorption of this aluminium oxide powder is not measurable (no detectable end point).
This pyrogenically produced aluminium oxide may be produced using the flame oxidation or preferably the flame hydrolysis method, wherein the starting material used is a vaporisable aluminium compound, preferably the chloride. This aluminium oxide is described in DE 199 42 291.0-41, incorporated herein by reference.
The present invention also provides granules based on pyrogenically produced aluminium oxide having the following physicochemical characteristics:
The granules according to the invention may be produced by dispersing pyrogenically produced aluminium oxide in water, spray drying it, optionally heat treating the granules obtained at a temperature of 150 to 1000xc2x0 C. for a period of 1 to 8 hours and then silanizing them.
Silanization may be performed using halosilanes, alkoxysilanes, silazanes and/or siloxanes.
The following substances may in particular be used as organosilanes:
The dispersion in water may exhibit an aluminium oxide concentration of 3 to 25 wt. %.
Organic auxiliary substances may be added to the dispersion in order to increase the stability of the dispersion and to improve particle morphology after spray drying.
The following auxiliary substances may, for example, be used: polyalcohols, polyethers, fluorocarbon-based surfactants, alcohols.
Spray drying may be performed at a temperature of 200 to 600xc2x0 C., using disk atomisers or nozzle atomisers, such as for example a single-fluid or two-fluid nozzle.
Heat treatment of the granules may be performed both in a stationary bed, such as for example in chamber kilns, and in a moving bed, such as for example rotary tube dryers.
Silanization may be performed with the same halosilanes, alkoxysilanes, silazanes and/or siloxanes as described above, wherein the silanising agent may optionally be dissolved in an organic solvent, such as for example ethanol.
The silanes trimethoxyoctylsilane, hexamethyldisilazane, aminopropyltriethoxysilane, dimethylpolysiloxane, hexadecyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane may preferably be used as the silanising agent.
Silanization may be performed by spraying the granules with the silanising agent at room temperature and then heat treating the mixture at a temperature of 105 to 400xc2x0 C. for a period of 1 to 6 hours.
Silanization of the granules may alternatively be performed by treating the granules with the silanizing agent in vapour form and then heat treating the mixture at a temperature of 200 to 800xc2x0 C. for a period of 0.5 to 6 h.
Heat treatment may be performed under protective gas, such as for example nitrogen.
Silanization may be performed continuously or batchwise in heatable mixers and dryers with sprayers. Suitable apparatuses may be, for example: plough bar mixers, disk dryers, fluidized or turbulent bed dryers.
By varying the feedstock, the conditions during spraying, heat treatment and silanization, it is possible to modify the physicochemical characteristics of the granules, such as specific surface area, grain size distribution, tamped density and pH value, within the stated ranges.
The aluminium oxide granules according to the invention exhibit the following advantages:
Flow behaviour is better than for aluminium oxide which has not been spray dried.
Incorporation into organic systems is easier.
Dispersion is simpler.
No additional auxiliary substances are required for granulation.
In comparison with aluminium oxide which has not been spray dried and does not exhibit a defined agglomerate size, the aluminium oxide granules according to the invention have a defined particle size.
The aluminium oxide granules according to the invention make dust-free handling possible.
Due to the elevated tamped density, transport packaging costs are reduced.
The aluminium oxide granules according to the invention may be used as a catalyst support.
Aluminium oxide which has not been spray dried is not suitable for this purpose because it is, for example, entrained from the fluidized bed.
The granules according to the invention may be used as supports for catalysts, and in cosmetics, in toner powders, in paints and lacquers, as abrasives and polishing agents and as a raw material in the production of glass and ceramics.
The granules may be modified in various ways.
Examples of Modification are:
Incorporation of cations, such as for example H+, Cs+, rare earth metal or noble metal cations.
Incorporation of materials or metal oxides by reaction with suitable precursor molecules, such as for example TiCl4, TiBr4, Ti(OEt)4, TiCp2Cl2 (Cp=cyclopenta-dienyl), Mn2(CO)10, Fe(CO)5.
Incorporation of noble metals or metal oxides by impregnation with solutions of the metal or noble metal salts.
The granules according to the invention may be used as catalysts and catalyst supports, for example for the following catalytic reactions:
Oxy-functionalization of hydrocarbons, oxidation of olefins to yield epoxides with hydrogen peroxide, alkyl or aryl hydroperoxides, such as for example tert.-butyl hydroperoxide or phenylethyl hydroperoxide (C6H5CH2CH2OOH) and/or oxygen, alkylation of aromatics, hydrogenations, dehydrogenation, hydration, dehydrations, isomerizations, addition and elimination reactions, nucleophilic and electrophilic substitution reactions, hydroxylations of aromatics and heteroaromatics, epoxy/aldehyde rearrangements, amminations, ammoximations, polymerization reactions, esterification and etherification reactions, as well as catalytic nitrogen oxide removal.
The granules according to the invention are moreover suitable as supports for dyes, perfumes and active substances.